Over the last decade SIDS research has shown that child care practices hold the most potential for reducing population risks for SIDS and that infant arousability may play a role in the mechanism(s) of SIDS. Our group has investigated the effects of parent-infant cosleeping (bedsharing) on infant sleep physiology as pertains to known risk factors and proposed mechanisms for SIDS. Bedsharing mother-infant pairs typically sleep in a face-to-face orientation at very close range which seems to facilitate sensory exchange and infant arousal. We hypothesize that the bedsharing infant experiences a slightly hypercapnic (nonlethal) environment, at least in part from the mother's exhalations and that infant respiration will be stimulated as a result. Also, there is evidence that when bedding is pulled up to the infant's face, an air pocket is formed around the infant's head, which leads to further hypercapnia. The proposed study will measure the infant's CO2 environment while napping at close face-to-face range with the mother and the respiratory responses to those CO2 levels. Twenty pairs of mothers and infants that have bedshared since birth and 20 pairs that have slept solitarily since birth will be studied under close face-to-face bedsharing and control conditions. The primary aim is to measure the effect of expired maternal CO2 on infant respiratory control, including tidal volume, minute ventilation, apnea and CO2 responsiveness. We hypothesize that the infant's environment will be slightly hypercapnic and that, as a result, infant tidal volume and minute ventilation will be increased. Long-term effects of any hypercapnia will be assessed by comparing the respiratory responses in the two groups to comparable CO2 levels. These comparisons will detect any habituation or sensitizatiOn, which in turn could increase or decrease arousal threshold, respectively. The proposed studies contribute important findings to SIDS research and also challenge a previously held conceptualization among infant researchers that "normal" infant sleep environment.